Particularly in regard to the manufacture of, and the fitment of components to, fuel tanks of plastic material which are produced by extrusion blow molding, the installation of functional components and holding them in the appropriate position often gives rise to problems. Such functional components that may be considered include for example vent valves, roll-over valves, senders, lines and the like. Those components have to be positioned and fixed within the fuel tank. As fuel tanks of plastic material are to be very substantially impermeable and sealed in relation to liquid hydrocarbons it is not possible to envisage the use of fixing procedures in which the tank wall has to be violated. For that reason therefore such components are generally welded with special holders to the inside wall surface of the fuel tank, more specifically generally in the immediate proximity of a relatively large assembly opening in the fuel tank. Finally, an assembly opening which is then to be welded shut so as to afford gas-tight and liquid-tight sealing integrity can also serve to accommodate holders for functional components of that nature.
Openings which are systematically provided in a fuel tank and which could serve for fixing functional components in position, such as for example an assembly opening or a filler opening should be reduced if possible to a minimum as such openings constitute potential weak points in the system in terms of sealing integrity.